The present invention relates to a radio receiving apparatus and a radio receiving method, and particularly to a radio receiving apparatus and a radio receiving method, which perform AGC (Auto Gain Control) to a received signal.
AS conventional AGC, one that can follow gentle and sharp variations in the level of a received signal due to fading by use of two kinds of time constants as disclosed in Unexamined Japanese Patent Publication HEI 8-274558. Also, the conventional AGC is performed based on an average level for one slot of the received signal.
However, performance of AGC based on the average level for one slot includes a problem in which an appropriate AGC gain value cannot be calculated when a data portion and a pilot portion (known signal portion), each having a different reception level, exist in one slot. Namely, in the TDD (Time Division Duplex) radio communication system where each of a reception channel and a transmission channel is assigned to a different time slot, the data portion normally accounts for about 4/5 in one slot. Hence, when the reception level of the pilot portion is higher than that of the data portion, the reception level of the pilot portion becomes higher than the average level of one slot. As a result, the level of the pilot portion subjected to AGC is clipped in some cases.
When such clipping occurs in this way, demodulation cannot be correctly performed. Since the pilot portion is used to estimate the propagation path characteristic, occurrence of clipping with respect to the pilot portion makes it impossible to estimate/compensate for phase variation of the data portion and amplitude variation thereof, with the result that not only the pilot portion but also the data portion cannot be correctly demodulated.
Additionally, clipping refers to the point in which the reception level of the received signal exceeds an input allowable range of A/D conversion, whereby preventing appropriate A/D conversion from being provided to the received signal that has exceeded the allowable range and resulting in the lost of a part of data.
An object of the present invention is to provide a radio receiving apparatus and a radio receiving method, which can calculate such an appropriate level control value (AGC gain value) that prevents occurrence of clipping to perform demodulation correctly even if portions each having a different reception level exist in a transmission unit (one slot).
In order to attain the above object, the present invention is configured to calculate a level control value using the highest reception level when a plurality of portions each having a different reception level exists in a transmission unit (one slot). This makes it possible to prevent clipping from being generated by AGC.